The effect of admixtures in concrete containing manufactured sand

Abstract

This project investigates the effects that varying water cement ratios and superplasticiser
have on concrete containing manufactured sand as a complete replacement for natural
sand. Due to current levels of construction in Australia there is an ever decreasing
availability of natural sands suitable for use as a fine aggregate in concrete. Manufactured
sands which are a by-product of rock crushing operations offer a viable solution to the
declining availability of natural sands. However there are a number of drawbacks to the
use of manufactured sand, particularly the poor workability and finish obtained. This is
caused by the High fines content (<75 microns) and the irregular particle shape of the
manufactured sand. For these reasons manufactured sand has a very poor reputation in
the construction industry.
An experimental approach has been taken to study the effect of the varying water cement
ratios and the effect of the superplasticiser. This has be done by making a number of
concrete mixes each with either a different water cement ratio or amount of
superplasticiser added to the mix. The properties of these concrete mixes have been
assessed by measuring both the fresh and hardened state properties of the concrete mix.
The results of the tests have shown that a reasonable workability and a medium strength
can be achieved with a high water cement ratio in a concrete mix. The addition of a
superplasticiser to a concrete mix allows the mix to achieve a high strength while also
having a good workability.